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RELAP5-3D

#18 of 18 in Simulation & CAE Software

RELAP5-3D: A specialized code for 3D reactor thermal-hydraulics and accident analysis. Ranked #18 of 18 in Simulation & CAE Software by our editors (7.1/10); pricing: Paid; best for nuclear teams modeling reactor thermal hydraulics.

7.1/10Editor score
Visit INL
RELAP5-3D7.1 Visit INL

At a glance

  • Editor score
    7.1 / 10
  • Pricing
    Paid
  • Best for
    Nuclear teams modeling reactor thermal hydraulics
  • Free plan
    No
  • Cloud access
    Both
  • Founded
    1979 · Idaho Falls, Idaho, United States
  • Facts checked
    25 Sep 2026

  • Where it wins

    • Models normal operation and accident scenarios across multiple reactor types
    • Supports 31 fluids and three-dimensional thermal-hydraulics modeling
    • Offers remote INL HPC or local executable access by license level

  • Where it doesn't

    • Focused on nuclear and related modeling, not broad CAE workflows
    • Organizational licensing and approval are required for access
    • License fees vary by level and domestic or international status

Our verdict on RELAP5-3D

RELAP5-3D is a thermal-hydraulics modeling and simulation code from Idaho National Laboratory for nuclear reactor behavior. It is aimed at teams working on reactor safety analysis, design, operator training, and reactor-system transients, rather than general-purpose CAE users. Its scope spans light-water, gas-cooled, molten-salt, and liquid-metal-cooled reactors, and it models normal operation as well as accident scenarios. The published plans show paid licensing, with no free plan.

The technical focus is three-dimensional thermal-hydraulics with integrated reactor kinetics. The code models 31 fluids and supports coupling with other codes through PVM, in-memory, socket, and Python methods. INL lists example coupled CFD codes including openFOAM and STAR-CCM+; that does not establish formal product integrations. This breadth across reactor types and coupling methods makes it relevant to nuclear analyses that need system-level transients or accident scenarios, but its specialization is a constraint for teams seeking a broader simulation suite.

Access and deployment depend on license level. According to the vendor's published plans, options range from Academic and single- or multi-user commercial licenses to Silver, Gold, and Platinum tiers. Level 1 provides HPC access; Level 2 provides a local executable; Silver offers restricted subroutine access through INL HPC; Gold and Platinum include source code access. Use requires an organizational license, export-control review, and approval for each user. Teams should choose RELAP5-3D when nuclear reactor thermal-hydraulics is central to the work and its licensing model fits; teams needing general-purpose CAE or unrestricted self-service access should consider alternatives.

Your product? Our editors can test RELAP5-3D in depth and publish a review, labelled as paid · from $149/mo →

RELAP5-3D pricing

Plans Paid No free plan — trial or paid only. Prices checked 25 Sep 2026.
See plans on inl.gov

All 8 RELAP5-3D plans and prices →

RELAP5-3D fact sheet

Free planNo
Paid fromNot verified
Simulation typesThermal-hydraulics; reactor-system transients and accident analysis; nuclear reactor kinetics
Solver typesThree-dimensional hydraulics; integrated thermal-hydraulic and kinetic modeling
Cloud accessBoth
Supported platformsLinux; Windows; INL high-performance computing
CAD file formatsNot verified
Deployment optionsBoth
DeploymentCloud, Self-hosted
PlatformsWindows, Linux
SupportEmail
Built forMid-market, Enterprise (editorial estimate)
Integrations2 integrations: openFOAM, STAR-CCM+
PricingPaid (source)
Websiteinl.gov
Facts checked25 Sep 2026

RELAP5-3D integrations

RELAP5-3D lists 2 integrations on its own site.

  • openFOAM
  • STAR-CCM+

Alternatives to RELAP5-3D

See all RELAP5-3D alternatives →

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Featured on iTechGuides

Featured on iTechGuides — RELAP5-3D 7.1/10

RELAP5-3D is listed in our Simulation & CAE Software directory. Add the badge to your site — it links back to this page.

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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

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